The present invention relates to a novel process for hydrogen processing of hydrocarbon feedstocks. More particularly, this invention relates to the use of a coated catalyst to reduce the sulfur, nitrogen and metal content of hydrocarbon feedstocks.
The preparation of surface-coated catalysts containing active catalytic oxide materials is disclosed in U.S. Pat. No. 4,077,912. This patent does not disclose that these coated catalysts are especially effective in hydrogen processing operations.
Hydrogen processing is a general term covering refinery processes with one thing in common--the use of hydrogen to improve hydrocarbon feedstocks. Processes of this type are hydrocracking, hydrogen refining and hydrogen treating.
Hydrogen processing of hydrocarbon feedstocks is well known in the art. For example, see Hydrocarbon Processing, pages 151 through 155 (August, 1977), and S. C. Schumann and H. Shalit, Catal. Rev. 4(2), 245 (1970). As can be seen from the art, these reactions normally involve the use of catalysts consisting of support materials impregnated with various catalytically active ingredients. Alternatively, the active ingredients and support are prepared together.
It is well known to those skilled in the art that there are several disadvantages with the prior art hydrogen processing reactions. First, hydroprocessing catalysts are deactivated by the deposition of metals, derived from organometallic components of the feed, on the outer portion of the catalyst particles. This is particularly true in the case of lead deposits on naphtha treating catalysts, vanadium deposits on catalysts for the hydrotreating of atmospheric gas oil, vacuum gas oils and vacuum residue, and iron sulfide deposits on catalysts for the hydrorefining of coal liquids and coal slurries.
Also, heat transfer limitations can be critical in hydrocracking operations involving highly exothermic reactions. With the catalysts of the prior art, excessive heat build-up in the interior of the catalyst particles leads to poor selectivity and the possibility of runaway exotherms.
The present invention is designed to alleviate these problems by the use of a coated catalyst as at least part of the reactor charge. Furthermore, although the activity of the coated catalyst would be comparable to a conventional catalyst, the catalyst cost would be substantially reduced since a large percentage of the reactor volume is being occupied by relatively cheap inert support.
In those reactions where the catalyst is deactivated by the formation of metal deposits on the catalyst surface, it would be extremely advantageous to replace at least a portion of the conventional hydrogen processing catalyst with a coated catalyst. The coated catalyst could be placed near the reactant inlet and serve as a repository for the undesirable metals in the feedstocks. Periodically, the coated catalyst could be replaced by fresh coated catalyst charge. Since the coated catalyst contains less of the active catalytic material than prior art catalysts, replacing coated catalyst would be less expensive than replacing prior art catalysts.
Finally, by employing coated catalysts in a hydrogen processing operation, one can achieve high heat transfer efficiency and thus maximize the control of selectivity and exotherm in the reactor.